Plastic eyeglass lenses have been known and have been in common use for many years. They have two principal advantages, namely they are light weight as compared to equivalent optical glass lenses and they meet state requirements as safety glasses. The primary disadvantage of plastic lenses is that they are easily scratched in normal use and these scratches interfere with their primary function of providing clear vision. Another disadvantage of plastic lenses is that they are difficult to tint in their normal state.
Lens manufacturers have developed very thin proprietary coatings that protect the plastic lens from scratching in normal use and that provide a means for tinting. These coatings are manufactured to be photosensitive to ultraviolet radiation and can be cured to a hardened state by exposure to the proper wave lengths at the proper intensity for a precise time. The hardness, durability and optical properties of the coating depend on precise exposure to ultraviolet radiation. Therefore machines for curing optical lens coatings must be capable of accuracy in radiation intensity, radiation wave lengths and in time of exposure to radiation. Speed of processing is also an important parameter because cycling time directly affects the cost of processing.
The inventors have found that there were commercially available machines for curing photosensitive protective films applied to eyeglass lenses but they were very expensive. They designed a compact apparatus that used state-of-the-art electronics to precisely control cycle parameters such as lens transport speed and radiation exposure time. They developed a special radiation collimator which intensified the lens deposited radiation allowing use of a lower power and less expensive ultraviolet lamp. The apparatus was designed so that the lenses were loaded, transported through the apparatus and unloaded in an inverted position so that dust and dirt would not settle on the coated surface. They also used protective door position sensors to assure operator safety by automatically preventing escape of radiation into the workspace.
The inventors have also researched the literature and discuss the following patents which may be construed as having somewhat similar function:
1. U.S. Pat. No. 3,826,014 by Helding describes an apparatus for ultraviolet curing of solvent free ink by photopolymerization. A reflector behind each lamp directs radiation towards the transport "web" belt. It has a light absorbing shutter in front of each lens that automatically opens and an air duct to cool the lamp terminals and draw off ozone and heated gases. This use of a reflector behind the ultraviolet lamp to direct radiation from the rear of the lamp to the front is not new and has been known from the time of wax candles. The inventors do not claim any novelty in the use of such a rear reflector. This referenced patent does disclose a light absorbing shutter in front of each lens to block escape of radiation to a moving transport belt if desired. Again, this application of a shutter to block unwanted radiation is not novel and has been used in motion picture projectors, cameras, naval signal lamps and the like for many years. In the present invention, an automatically controlled door and shutter are used to prevent escape of radiation from a radiation chamber as a regular part of the process for operator safety and for exposure control. PA1 2. U.S. Pat. No. 3,950,650 by Pray & Foster, discloses an apparatus for ultraviolet curing of solvent free ink by photopolymerization. A reflector behind each lamp directs radiation towards the transport "web" belt. Cooling air passages are designed to cool terminals, reflectors, etc. without cooling the ultraviolet lamp body. This system of cooling terminals, reflectors, etc. has been and is in common use in motion picture and slide projectors. Its use in conjunction with an ultraviolet lamp is not novel and the present invention treats cooling of these items as a standard engineering practice. PA1 3. U.S. Pat. No. 4,471,226 by Wisnosky, discloses an improved safety housing for a radiation source with mechanical interlocks to prevent activation of the source unless the protective shield is in place. This reference differs from the present invention because in the present invention the radiation source is continually actuated and two automatically actuated doors in series with each other are prevented from opening at the same time by electrical controller logic which obtains individual door open/close status from individual position sensors. Therefore safety is obtained by assuring that at least one door is always completely shut at all times while the radiation source is energized.